* {
  box-sizing: border-box;
}

html,
body {
  height: 100%;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  margin: 0;
  font-family: sans-serif;
}

fieldset {
  border: 0;
  margin: 0;
  padding: 0;
}

.a11y {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  opacity: 0;
  font-size: 1px;
  line-height: 1;
  white-space: nowrap;
}

.container {
  overflow: hidden;
  width: 300px;
  color: #fff;
  background: #57585a;
  border-radius: 4px;
}

.calc button {
  border: 0;
  padding: 0;
  color: #fff;
  font-size: 24px;
  outline: none;
}

#output {
  display: block;
  padding: 0 16px;
  height: 96px;
  line-height: 96px;
  font-size: 42px;
  white-space: nowrap;
  text-align: right;
}

#input {
  display: flex;
  flex-flow: column wrap;
  height: calc(65px * 5);
}

#actions {
  display: flex;
  width: 75%;
  height: 20%;
}

#actions button {
  width: calc(33.33% - 1px);
  margin: 0 1px 1px 0;
  background: #656769;
}

#numbers {
  display: flex;
  flex-flow: wrap;
  width: 75%;
  height: 80%;
}

#numbers button {
  width: calc(33.33% - 1px);
  height: calc(25% - 1px);
  margin: 0 1px 1px 0;
  background: #808082;
}

#numbers button.zero {
  width: calc(66.66% - 1px);
}

#operators {
  display: flex;
  flex-flow: column;
  width: 25%;
  height: 100%;
}

#operators button {
  height: calc(20% - 1px);
  margin-bottom: 1px;
  background: #fca02b;
}